Often expressed and deeply felt, Aristotle's complaint that Plato's philosophy does not recognize change or try to make sense of it is not wholly without justification. Plato draws an opposition between what really is and what becomes. These are two categories of things that, in the most striking expression of his thought, exclude each other. There are the things that really exist (the Forms) and the things that change and are in their nature unstable (the particulars). Only the first kind are objects of real knowledge; the other things are at best objects of belief and perception.

Aristotle complains that if, according to this dichotomous metaphysics, we want to understand the nature of some particular kind of animal, for example, we should ignore the fact that animals are self-movers and say nothing about the specifics of how they move. Nor should we take any interest in their birth or death, or their growth, since all these phenomena are on the side of change. The relevant Form is the only thing that can reveal the subject's nature; and it does so by virtue of remaining an utterly immobile object. Even such things as values, Aristotle maintains, are misconstrued by Plato. The good that we humans want to pursue is what is good for human persons, not some metaphysical entity that transcends the world in which we live and move.